It is well known that crystalline polypropylene generally has an isotactic or syndiotactic structure and that amorphous polypropylene generally has considerable atactic structure. U.S. Pat. Nos. 3,112,300 and 3,112,301, for example, describe isotactic polypropylene and provide structural formulae for isotactic and syndiotactic polypropylene. The former is a straight chain of propylene units wherein the methyl groups are all aligned on one side of the polymer chain. In the latter, the methyl groups alternate from one side of the chain to the other. In these polypropylenes, the regularity of structure tends to result in a more highly crystalline material. Historically, atactic polypropylene polymers have a low MW, typically resulting in gummy materials of minimal tensile strength.
High-molecular-weight amorphous poly alpha-olefins ("APAO"), such as amorphous propylene homo- and co-polymers, are important for their use in diverse products. The broad utility of these materials is due in large part to the unique combination of chemical and physical properties, such as chemical inertness, softness, flexibility, etc., exhibited by these materials. Amorphous polypropylene is different from crystalline polypropylenes in steric microstructure.
Almost all of the polypropylene which is used commercially is crystalline isotactic polypropylene. Conventional polymers of this type typically have a crystallinity, or heat of fusion, of 70 J/g or higher, and more typically 90 J/g or higher. These products are well known and have been the subject of many patents and articles.
The below-mentioned patents disclose one type of catalyst used in the formation of such polymers, which includes a pro-catalyst that is typically formed from the reaction product of a magnesium alkoxide compound, preferably one of the formula MgR.sub.1 R.sub.2, where R.sub.1 is an alkoxy or aryl oxide group and R.sub.2 is an alkoxide or an aryl oxide group or halogen, and a tetravalent titanium halide wherein the reaction takes place in the presence of an electron donor and, preferably, a halogenated hydrocarbon.
U.S. Pat. No. 5,118,768 discloses a process for the production of elastomeric, primarily isotactic polyolefins by polymerizing olefins in the presence of a catalyst which includes: (a) the reaction product of a magnesium alkoxide having a formula of MgR.sub.1 R.sub.2, where R.sub.1 is an alkoxy or aryl oxide group and R.sub.2 is an alkoxide or an aryl oxide group or halogen and a tetravalent titanium halide and wherein the reaction takes place in the presence of an electron donor that is an effectively hindered heterocyclic aromatic nitrogen compound, and (b) an organoaluminum compound. A variety of electron donors are disclosed, including 2,6-lutidine and 6-chloro-2-picoline. U.S. Pat. No. 5,164,352 has an identical disclosure, but it is directed to the catalyst used in the polymerization of these polyolefins. Both references disclose that the catalyst production occurs in a liquid reaction medium, which must be followed by elaborate steps to suitably isolate the catalyst from the reaction solvent(s). The polymerization reaction also occurs in the liquid phase at a temperature of 50.degree. C. to 80.degree. C. and a pressure sufficient to maintain liquid conditions.
U.S. Pat. Nos. 5,089,573, 5,118,649, 5,118,767, and 5,294,581, all similarly require magnesium alkoxide and/or magnesium aryl oxide. These references are substantially similar to U.S. Pat. Nos. 5,118,768 and 5,164,352.
U.S. Pat. Nos. 5,438,110 and 4,990,479 disclose a polymerization process that involves polymerizing or copolymerizing olefins in the presence of an olefin polymerization catalyst formed from: (A) a solid titanium component which contains magnesium, titanium, halogen and an electron donor as the essential components, where the magnesium compound or magnesium compound with the electron donor is reacted with titanium in the liquid phase, (B) an organoaluminum compound, and (C) an organosilicon compound represented by the formula SiR.sup.21 R.sup.22.sub.m (OR.sup.23).sub.3-m, where R.sup.21 is a cyclopentyl group, a substituted cyclopentyl group, or one of several other ringed structures.
U.S. Pat. No. 5,218,052 discloses a method for making a homopolymer of propylene having increased stiffness and a broadened, molecular weight distribution by polymerizing propylene in a high activity catalyst system and a silane in at least two stages. That system includes: (a) a silane of formula R.sub.1 (R.sub.2).sub.x Si(OR.sub.4).sub.y (OR.sub.5).sub.z ; (b) a titanium-containing compound supported on a magnesium-containing compound; and (c) a co-catalyst comprising a Group II or III metal alkyl. Lutidine is disclosed among a vast genus of possible electron donors.
U.S. Pat. No. 5,182,245 discloses a solid, hydrocarbon-insoluble catalyst or catalyst component for the polymerization of alpha-olefins in the slurry phase, from a product produced by: (A) forming a solution of magnesium-containing species in a liquid, (B) precipitating solid particles from the solution by treatment with a transition metal halide in the presence of at least one of a tetrabutoxysilane and a tetrabutoxytitanate; and (C) treating the particles with a transition metal compound and an electron donor. Lutidine is disclosed as a possible electron donor among a vast genus of possible electron donors.
U.S. Pat. No. 5,153,158 discloses: (I) an olefin polymerization catalyst formed by prepolymerization of olefin and an olefin polymerization catalyst of a solid titanium catalyst component (A) having magnesium, titanium, and halogen as essential ingredients, along with (B) a Group I or III metal organometallic compound and (C) an electron donor selected from diethers and organosilicons represented by R.sub.n Si(OR').sub.4-n, and being suspended in a liquid alpha-olefin, and (II) a metal organometallic compound of a Group I or III metal. The R.sub.1 group is disclosed in the specification to be one of various cyclopentyl or substituted cyclopentyl groups. U.S. Pat. No. 4,990,477 is essentially cumulative, except that it discloses that the optional electron donor may instead be an organic carboxylic acid.
European Patent 475,307 discloses an elastomeric high molecular weight substantially amorphous propylene homopolymer having a melting point between about 145.degree. C. and 165.degree. C., a melt viscosity at 190.degree. C. of greater than 200,000 cPs, a heat of fusion of about 16.7 J/g to 41.8 J/g, having about a 35% to 55% diethyl ether soluble fraction, which fraction has inherent viscosity less than about 1.0 dl/g and is substantially free of isotactic crystallinity.
Amorphous polypropylenes, which have very little strength, are used commercially in adhesives and asphalt additives, for example. Conventional amorphous polypropylenes that tend to have a crystallinity lower than 65 J/g typically have an extremely high melt flow rate of around 10,000 g/10 min. (at 230.degree. C.). Generally, these amorphous polypropylene polyolefins are sticky, which limits their possible usage in commercial products. Conventional heterogeneous Ziegler-Natta catalysts, such as those disclosed in U.S. Pat. No. 4,347,158, for example, tend to produce tacky polymers that have a broad range of molecular weights and tacticities. It would be advantageous to reduce this stickiness in the polyolefins and to produce polyolefins having a low degree of crystallinity and a lower melt flow rate, thereby creating a class of polymers having a variety of new uses.
It is thus desired to produce higher molecular weight FPO polymers that have a low crystallinity, low solubility in methylethyl ketone, and a low melt flow rate ("MFR").